Slorvex

Hello I just purchased a 1994 Chevy Cheyenne 2500HD 5.7 TBI. The guy I bought it off of , said the motor was replaced, and I would need the hookups to connect the o2 sensors. Well sounded like an easy fix. So I went to local junk yard crawled under truck, found 3 o2 sensors with wires hanging, but no where to plug them into factory wire harness. I've look all over and can't figure out where they where cut, or as to why. When it's first started it rough as Hell but smoothes out within 5-10 seconds. Runs smooth and you can't tell it's running. It's burning rich obviously, and want to fix this problem. So how would I go about tracking down where the o2 sensors plug into. Does the o2 wires come out of the computer? I would like to make my own plugs if possible without buying $450 factory wire harness. I just need help with this problem or suggestions. Not sure if running in limp mode is bad for the computer.